The invention relates to a device for determining the load acting on the body of a vehicle occupant restrained by a seat belt, wherein electrical signals from occupant restraint device sensors are evaluated in an evaluating device.
DE 297 17 477 U1 teaches a seat belt retractor in which the winding state of the seat belt is determined by a belt reel sensor, which, acting as an incremental sensor, detects the rotational position of the belt reel. The corresponding signals are fed together with other sensor signals to an electronic unit present in the vehicle, which contains a microcomputer with microprocessor and associated memories, for evaluation of the signals. Depending on the signal evaluation, given safety devices of the vehicle occupant restraint system, such as a belt tightener, an airbag, a belt buckle and the like are actuated.
It is known from WO 85/04628 to trigger the blocking device, with which the belt reel is blocked in the seat belt retractor, as a function of rotational angle signals that are obtained from scanning of the belt reel.
It is further known from U.S. Pat. No. 6,290,159 B1 to adjust the restraining force of a belt force limiter as a function of signals obtained from scanning of the rotating movement of the blocked belt reel.
In the present invention the movement of the webbing of the seat belt caused by the body of the belted-in vehicle occupant is scanned and a corresponding electrical signal is fed to the evaluating device. The webbing movement may be a webbing movement directed in the webbing take-up direction by a belt tightener drive or a webbing extraction movement. The webbing extraction movement may be caused by forward displacement of the belted-in vehicle occupant or by a webbing extraction movement effected manually by the vehicle occupant. The webbing extraction movement effected in particular by forward displacement, for example by increased acceleration, may be effected against a restraining force with a given force characteristic curve. The force characteristic curve may correspond substantially to the profile of a spring force characteristic curve. Scanning is preferably performed of webbing movement that takes place against the restraining force of a force limiter in which energy is absorbed by material deformation. Such a belt force limiter may take the form of a torsion bar, which is arranged inside the belt reel. Such a belt force limiter is known from U.S. Pat. No. 6,290,159 B1 for example.
There is provided in accordance with the present invention a vehicle occupant restraint system for a vehicle comprising a seat belt retractor for a seat belt, a belt tightener drive, the drive moment of which may be transmitted by a rotor to the belt reel of the seat belt retractor, wherein a torque transmission device exhibiting a given damping behavior transmits the drive moment to the belt reel and a rotational angle sensor supplies an electrical signal corresponding to a rotational angle of the belt reel to an evaluating device that determines from the electrical signal and the damping behavior a force acting upon torque transmission between the seat belt and a belted-in vehicle occupant.